Aircraft gas turbine propulsion engines and auxiliary power units (APUs) provide cabin environmental control air from an engine air compressor. A leak in the turbine engine seal system can introduce oil in to this air. This can cause an oil smell in the cabin as well as cause cabin environmental issues. Since multiple engines supply cabin air during the aircraft operating cycle, it is difficult to diagnose the source of cabin air contamination. This may result in removal of the wrong engine and persistence of the problem.
To date, various methods of detecting oil in bleed air of turbine have been explored, including the measurement of hydrocarbon content in the air by flame ionisation detector, filter paper collection and detection with ultraviolet light, and sniff panels. None of these methods have proven to be useful in determining the presence of oil in the bleed air. The only practical method of detecting a leak in the rotor shaft seal system has been to look for evidence of oil discharging from the compressor shroud bleed slots during as-received acceptance test procedure evaluation or disassembly of the engine and inspection of seal system components.
The hydrocarbon analyser and filter paper methods have proven to be too insensitive to detect concentrations of oil that are of concern. The filter paper test has the additional disadvantage of not being a real time measurement. “Sniff panels”, where a group of people smell the bleed air, have proven to be ineffective. Since oil in the bleed air is not decomposed and oxides of sulphur are not present, oil is not easily detected by this method.